Abstract
We study the kinematics and excitation mechanisms of molecular hydrogen and [Fe II] lines in a sample of 67 emission-line galaxies with Infrared Telescope Facility SpeX near-infrared (NIR) spectroscopy together with new photoionisation models, in the wavelength interval between 0.8μ m and 2.4μ m. H_{2} emission lines are systematically narrower than narrow-line region (NLR) lines, suggesting that both are, very likely, kinematically disconnected. The new models and emission-line ratios show that the thermal excitation plays an important role not only in active galactic nuclei but also in star forming galaxies. The importance of the thermal excitation in star forming galaxies may be associated with the presence of supernova remnants close to the region emitting H_{2} lines. This hypothesis is further supported by the similarity between the vibrational and rotational temperatures of H_{2}. We confirm that the diagram involving the line ratios H_{2} 2.121μ m /Brγ and [Fe II] 1.257μ m /Paβ is an efficient tool for separating emission-line objects according to their dominant type of activity. New limits to the line ratios, are suggested, in order to discriminate between the different types of nuclear activity.
